The groundwork for theories of psychological type were laid in 1921 with Carl Gustav Jung's pioneering work "Psychological Types" (ISBN 0691097704). After its translation from German into English in 1923, Isabel Briggs Myers and her mother began studying Jung's work, and in 1942 they published the first version of a test intended to identify which type category a person fit into, named the Myers-Briggs Type Indicator (MBTI).

The following quotes are from prominent figures in the short history of psychological type who have based their theories, writings, and systemics on the four basic cognitive functions initially conceived of by Jung, which are sensing, intuition, thinking, and feeling. Each of these will be in a certain attitude, either introverted or extraverted. Notably, Jung did not have the dichotomy of Judgement / Perception, which is a theory of Myers, and Jung's attention to the Conscious and Unconscious are not made explicit in Myers' theories. There is also skeptical speculation that Jung did not approve of Myers' test.

"There is, finally, a third group, and here it is hard to say whether the motivation comes chiefly from within or without. This group is the most numerous and includes the less differentiated normal man" (Jung, 1971. Jung, C. G. (1971). Psychological types. In W. McGuire (Ed.) The collected works of C. G. Jung (Vol. 6), Bollinger Series XX. Princeton, NJ: Princeton University Press.)

When a function habitually predominates, a typical attitude is produced. According to the nature of the differentiated function, there will be constellations of contents that create a corresponding attitude.(Psychological Types by C G Jung : Para 691, Page 417)

Only a limited number of contents can be held in the conscious field at the same time, and of these only a few can attain the highest grade of consciousness. The activity of consciousness is selective. Selection demands direction. But direction requires the exclusion of everything irrelevant. This is bound to make the conscious orientation one-sided. The contents that are excluded and inhibited by the chosen direction sink into the unconscious, where they form a counterweight to the conscious orientation.(Psychological Types by C G Jung : Para 694, Page 419)

Just as there is a relation to the outer object, an outer attitude, there is a relation to the inner object, an inner attitude.(Psychological Types by C G Jung : Para 801, Page 466)

One cannot be introverted or extraverted without being so in every respect. For example, to be “introverted” means that everything in the psyche happens as it must happen according to the law of the introvert’s nature.(Psychological Types by C G Jung : Para 939, Page 534)

Introversion or extraversion, as the typical attitude, means an essential bias which conditions the whole psychic process, establishes the habitual mode of reaction, and thus determines not only the style of behaviour but also the quality of subjective experience. Not only that, it determines the kind of compensation the unconscious will produce.(Psychological Types by C G Jung : Para 940, Page 534)

But there is no energy unless there is a tension of opposites; hence it is necessary to discover the opposite to the attitude of the conscious mind.(Two Essays on Analytical Psychology by C G Jung : Para 78, Page 53)

The introvert does possess an extraverted attitude, but it is unconscious, because his conscious gaze is always turned to the subject.(Two Essays on Analytical Psychology by C G Jung : Para 81, Page 56)

…experience shows that there is only one consciously directed function of adaptation.(On the Nature of the Psyche by C G Jung : Line 15, Page 25)

The attitude of the unconscious as an effective complement to the conscious extraverted attitude has a definitely introverted character.(Psychological Types by C G Jung : Para 570, Page 337)

We call a mode of behaviour extraverted only when the mechanism of extraversion predominates. In these cases the most differentiated function is always employed in an extraverted way, where as the inferior functions are introverted; in other words, the superior function is the most conscious one and completely under conscious control, whereas the less differentiated functions are in part unconscious and far less under the control of consciousness.(Psychological Types by C G Jung : Para 575, Page 340)

I made a discovery that was shocking to me, namely the fact of this extraverted personality, which every introvert carries within him in his unconscious, and which I had been projecting upon my friends to their detriment.(Analytical Psychology by C G Jung : Line 1, Page 32)

Just as all energy proceeds from opposition, so the psyche too possesses its inner polarity, this being the indisputable prerequisite for its aliveness.(Memories, Dreams, Reflections : Line 22, Page 379)

The extravert’s [extraverted] feeling is always in harmony with objective values. … even when it appears not to be qualified by a concrete object, it is none the less still under the spell of traditional or generally accepted values of some kind. I may feel moved, for instance, to say that something is “beautiful” or “good”, not because I find it “beautiful” or “good” from my own subjective feeling about it, but because it is fitting and politic to call it so, since a contrary judgment would upset the general feeling situation. A feeling judgment of this kind is not by any means a pretense or a lie, it is simply an act of adjustment.(Psychological Types, CW6, paragraph 595. The Portable Jung, page 207)

"But one can feel “correctly” only when feeling is not disturbed by anything else. Nothing disturbs feeling so much as thinking." (Psychological Types, CW6, paragraph 598. The Portable Jung, page 209)

In so far as feeling is compliant and lets itself be subordinated, it has to support the conscious attitude and adapt to its aims. But this is possible only up to a point; part of it remains refractory and has to be repressed. (Psychological Types, The Extraverted Thinking Type, CW6, paragraph 588. The Portable Jung, page 200.)

"FEELING. I am unable to support the psychological school that considers feeling a secondary phenomenon dependent on "representations" or sensations, but … I regard it as an independent function sui generis" (723)

"Feeling is primarily a process that … imparts to the content a definite value in the sense of acceptance or rejection ("like" or "dislike")". (724)

"Even an "indifferent" sensation possesses a feeling-tone, namely that of indifference, which again expresses some sort of valuation. Hence feeling is a kind of judgment, differing from intellectual judgment in that its aim is not to establish conceptual relations but to set up a subjective criterion of acceptance or rejection. Valuation by feeling extends to every content of consciousness, of whatever kind it may be. When the intensity of feeling increases, it turns into an affect, i.e., a feeling state accompanied by marked physical innervations. Feeling is distinguished from affect by the fact that it produces no perceptible physical innervations, i.e., neither more nor less than an ordinary thinking process." (725)

"Ordinary, "simple" feeling is concrete, that is, it is mixed up with other functional elements, more particularly with sensations. In this case we call it affective or, as I have done in this book, feeling-sensation, by which I mean an almost inseparable amalgam of feeling and sensation elements. This characteristic amalgamation is found wherever feeling is still an undifferentiated function, and is most evident in the psyche of a neurotic with differentiated thinking. Although feeling is, in itself, an independent function, it can easily become dependent on another function – thinking, for instance; it is then a mere concomitant of thinking, and is not repressed only in so far as it accommodates itself to the thinking processes." (726) (Psychological Types, CW6, DEFINITIONS, paragraphs 723-726.)

Hence his thinking is of value for his contemporaries only so long as it is manifestly and intelligibly related to the known facts of the time. Once it has become mythological, it ceases to be relevant and runs on in itself. (Psychological Types, The Introverted Thinking Type, CW6, paragraph 637. The Portable Jung, page 244.)

"It should not be imagined that the unconscious lies permanently buried under so many overlying strata that it can only be uncovered, so to speak, by a laborious process of excavation. On the contrary, there is a constant influx of unconscious contents into the conscious psychological process, to such a degree that at times it is hard for the observer to decide which character traits belong to the conscious and which to the unconscious personality. … Naturally it also depends very largely on the attitude of the observer whether he seizes hold of the conscious or the unconscious character of the personality. … We must observe which function is completely under conscious control, and which functions have a haphazard and spontaneous character … the latter possess infantile and primitive traits.(Psychological Types, CW6, paragraph 576. The Portable Jung, pages 191-192.)

"Discrimination is the sine qua non of cognition. But discrimination means splitting up the contents of consciousness into discrete functions. Therefore, if we wish to define the psychological peculiarity of a man in terms that will satisfy not only our own subjective judgment but also the object judged, we must take as our criterion that state or attitude which is felt by the object to be the conscious, normal condition. Accordingly, we shall make his conscious motives our first concern, while eliminating as far as possible our own arbitrary interpretations."(Psychological Types, CW6, paragraph 891.)

"The term Inferior Function is used to denote the function that lags behind in the process of differentiation. Experience shows that it is practically impossible, owing to adverse circumstances in general, for anyone to develop all of his psychological functions simultaneously. The demands of society compel a man to apply himself first and foremost to the diffferentiation of the function with which he is best equipped by nature, or which will secure him the greatest social success. As a general rule a man identifies more or less completely with the most favored and hence the most developed function. It is this that gives rise to psychological types. As a consequence of this one-sided development, one or more functions are neccessarily retarded. These functions may properly be called inferior in a psychological, not a psychopathalogical sense, since they are in no way morbid but merely backward as compared with the favored function. Although the inferior function may be conscious as a phenomenon, its true significance nevertheless remains unrecognized. It behaves like many repressed or insufficiently appreciated contents, which are partly conscious and partly unconscious, just as, very often, one knows a certain person from his outward appearance but does not know him as he really is." C. G. Jung (1934). Psychological Types (pages 450-451)

We know, however, that the mind cannot be a tabularasa...certain categories of thinking are given a priori; they are antecedent to all experience and appear with the first act of thought, of which they are preformed determinants... The new-born brain is an immensely old instrument fitted out for quite specific purposes, which does not apperceive passively but actively arranges the experiences of its own accord and enforces certain conclusions and judgements. They are...a kind of pre-existent ground plan...or inherited functional possibilities which, nevertheless, exclude other possibilities or at any rate limit them to a very great extent. They are...like invisible stage managers behind the scenes. C.G. Jung (1934). Psychological Types (Section 512)

How fantasy is assessed by psychology, so long as this remains merely science, is illustrated by the well-known views of Freud and Adler. The characteristic animosity between the adherents of the two standpoints arises from the fact that either standpoint necessarily involves a devaluation and disparagement of the other. So long as the radical difference … is not recognized, either side must naturally hold its respective theory to be universally valid. (Psychological Types, CW6, paragraph 88.)

"In complete contrast to the old system of classification by temperaments, the new typology begins with the explicit agreement neither to allow oneself to be judged by affect nor to judge others by it, since no one can declare himself finally identical with his affect." (Psychological Types, CW6, PSYCHOLOGICAL TYPES lecture 1923, paragraph 889)

"… begin with the explicit agreement neither to allow oneself to be judged by affect nor to judge others by it … the affect is considered an exceptional state whose qualities are represented either as a falsification of the “real” personality or as not belonging to it as an authentic attribute. What then is the “real” personality? Obviously, it is partly that which everyone distinguishes in himself as separate from affect, and partly that in everyone which is dismissed as inauthentic in the judgment of others. … In the affective state it [the ego] is unfree, driven, coerced. By contrast, the normal state is a state of free will, with all one’s powers at one’s disposal. In other words, the affective state is unproblematical, while the normal state is problematical: it comprises both the problem and possibility of free choice. In this latter state an understanding becomes possible, because in it alone can one discern one’s motives and gain self-knowledge.(Psychological Types, CW6, paragraphs 889,891.)

" AFFECT. By the term affect I mean a state of feeling characterized by marked physical innervation on the one hand and a peculiar disturbance of the ideational process on the other. I use emotion as synonymous with affect. I distinguish … feeling from affect, in spite of the fact that the dividing line is fluid, since every feeling, after attaining a certain strength, releases physical innervations, thus becoming an affect. For practical reasons, however, it is advisable to distinguish affect from feeling, since feeling can be a voluntarily disposable function, whereas affect is usually not. Similarly, affect is clearly distinguished from feeling by quite perceptible physical innervations, while feeling for the most part lacks them, or else their intensity is so slight that they can be demonstrated only by the most delicate instruments ..." (Psychological Types, CW6, DEFINITIONS, paragraph 681.)

(Extraverted Feeling) "Its soundness and value do not lie in the individual, but outside in the collective ideals of the community, which are usually accepted without question. Its goal is the formation and maintenance of easy and harmonious emotional relationships with other people. "(Gifts Differing, by Isabel Briggs Myers, page 79)

"Introverted feeling types have a wealth of warmth and enthusiasm, but they may not show it until they know someone well. They wear their warm side inside, like a fur-lined coat." (Gifts Differing, by Isabel Briggs Myers, page 96)

"These basic differences concern the way people "prefer" to use their minds, specifically the way they perceive and the way they make judgements. "Perceiving" is here understood to include the processes of becoming aware of things, people, occurrences and ideas. "Judgment" includes the processes of coming to conclusions about what has been perceived. Together, perception and judgement make up a large portion of a person's total mental activity. They govern much of their outer behavior, because perception -- by definition -- determines what people see in a situation and their judgment determines what they decide to do about it. Thus it is reasonable that basic differences in perception or judgment should result in correpspdonding differences in behavior. (Isabel Briggs Myers (1980). Gifts Differing (page 1).

"A generally perceptive attitude is perfectly consistent with firm parental discipline. Discipline is needed to enforce the fundamentals, preferably a few fundamentals. If children observe those faithfully, they are acceptable members of society, and just like grown-ups, they are entitled to be spared a running commentary on their every act." (Isabel Briggs Myers (1980). Gifts Differing (page 72).

"This book is written in the belief that many problems might be dealt with more successfully if approached in the light of C.G. Jung's theory of psychological types. The first English translation of his Psychological Types was published by Harcourt brace in 1923. My mother, Katharine C. Briggs, introduced it into our family and made it part of our lives. She and I waited a long time for someone to devise an instrument that would reflect not only one's preference for extraversion or introversion, but one's preferred kind of perception and judgement as well. In the summer of 1942 we undertook to do it ourselves. Since then the Myers-Briggs Type Indicator has yielded a wide range of information about the practical bearing of type. (Isabel Briggs Myers (1980). Gifts Differing (Preface)

"In the darkest days of World War II when the Germans were rolling irresistibly along and my shoulders ached with trying to hold them back and a horrible sinking feeling lived in the pit of my stomach, the thought came to me one day (I was making my bed at the time) that by letting them spoil my life that I way I was helping them win, bringing destruction to pass by my own doing. So I stopped, just like that. I made up my mind that there was no logical justification for turning possible future unhappiness into certain present unhappiness by being afraid of it. Do what you can to make a better world, but don't throw away one day or one minute of the world you've got. What I did, as it turned out, was the Type Indicator (Isabel Briggs Myers (1970). Personal letter to Mary McCaulley)

"We know that Jung once told a colleague that his Dominant function was Introverted Thinking. That means he was either an ISTP or an INTP. Jung was certainly abstract rather than concrete, so it seems safe to hold him up as an example of an INTP." Vol. 2 No. 3 (Winter 1985) of The Type Reporter (page 10)

Between extraversion and introversion there is also a compensatory relation. Where consciousness is extraverted, the unconscious is introverted and conversely.(The Psychology of C G Jung by Jolande Jacobi : Line 34, Page 19)

The extravert has an introverted unconscious, though precisely because this side of him remains unconscious, its introversion takes on undifferentiated and compulsive or instinctual form.(The Psychology of C G Jung by Jolande Jacobi : Line 4, Page 20)

The psyche consists of two complementary but antithetical spheres: consciousness and the unconscious.(The Psychology of C G Jung by Jolande Jacobi : Line 5, Page 5)

Extraverted sensation + thinking as an auxiliary function. In this type……cooperation with the main function is made easier because of thinking’s similar attitude (extraversion).(Personality by C A Meier : Line 1, Page 32)

"So I have long believed that personality, like anatomy, comes about not by an integration of elements, but by differentiation within an already integrated whole, emerging gradually as an individuated configuration." David Keirsey, Please Understand Me II, page 31

"Extraverts look at a situation and ask, 'How do I affect that?'…Introverts tend to ask themselves, 'How does that affect me?'" (Just Your Type by Paul D. Tieger and Barbara Barron-Tieger, page 12)

"A man's disposition is like a mark in a stone, no one can efface it." ~ Anonymous